Filter cartridge having cone of visibility for end-of-service-life-indicator (esli)

ABSTRACT

A filter cartridge  12  that includes a filter material  42 , an end-of-service-life-indicator  40,  a cartridge housing  22,  and a window  38.  The filter material  42  and ESLI  40  are disposed in the housing, and the ESLI  40  may be viewed through the window  38.  The window  38  is configured such that the ESLI  40  can only be seen within a cone defined by an angle θ of 20 to 70 degrees. The limited viewing range precludes reader error when examining the ESLI for color change.

The present invention pertains to a filter cartridge that has a windowthrough which an ESLI may be viewed. The window provides a cone ofvisibility so that the viewer cannot see the ESLI from an angle thatcould provide an erroneous reading.

BACKGROUND

Filter cartridges are commonly attached to respirator mask bodies tofilter air before it is inhaled by the respirator wearer. Examples ofrespirator filter cartridges are shown in the following U.S. Pat. No.7,320,722B2 to Mittelstadt et al., U.S. Pat. No. 7,419,526 to Greer etal., and U.S. Pat No. 6,277,178 to Holmquist-Brown et al.

Some filter cartridges have an end-of-service-life-indicator, or ESLI,that provides a visible color-change signal to the respirator wearer.This visible signal (sometimes referred to as the “response signal”)indicates when the filter cartridge has met the end of its useful life.Examples of cartridges that use ESLIs are described in the followingU.S. Pat. Nos. 6,497,756, 4,530,706, 4,326,514, and 4,154,586. In eachof these products, the filter cartridges are provided with a transparentsidewall or a shell through which the ESLI may be viewed. ESLIcolorimetric sensors often exhibit a different color, depending on theangle from which the sensor is viewed. When a person does not view theESLI normal to its positioning on the filter cartridge, there is anopportunity for the viewer to misread the indicator. A misread indicatorcould cause the wearer of the respirator to replace the filter cartridgetoo early or too late. Known filter cartridges have allowed the viewerto see the ESLI from angles of about 180° and accordingly have notaddressed the issue of potential misread indicators.

SUMMARY OF THE INVENTION

The present invention provides a new filter cartridge that comprises:(a) a filter material; (b) an end-of-service-life-indicator (ESLI); (c)a cartridge housing into which the filter material and ESLI aredisposed; (d) a window through which the ESLI may be viewed, the windowbeing configured such that the ESLI can only be seen through the windowwithin a cone defined by an angle θ of 20 to 60 degrees.

As indicated above, known filter cartridges have used sensors that arevisible through the cartridge housing sidewall. These known filtercartridges have not, however, also provided a window that is configuredto enable viewing only from a selected range of angles. Presentinvention recognizes the problem presented by known filter cartridgesthat contain ESLIs and provides a solution. The solution involvesproviding a window that is configured such that the ESLI may only beviewed through a code of visibility that is defined by an angle omega of20 to 60°. Outside this range of visibility the viewer cannot see theESLI and therefore cannot see a color other than the color desired to beseen when the sensor is viewed perpendicular to its planarconfiguration.

Glossary

In this document:

“clean air” means a volume of atmospheric ambient air that has beenfiltered to remove contaminants;

“contaminants” means gases, vapors, and particles (including dusts,mists, and fumes) and/or other substances that generally may not beconsidered to be gases, vapors, or particles but which may be present inair and harmful to a person;

“end-of-service-life-indicator” or “ESLI” means a device that is capableof providing a person with information pertaining to when a filter mayno longer be suitable for use due to partial or full exhaustion of thefiltering capacity;

“extension” means the condition of significantly increasing size beyonda typical configuration;

“exterior gas space” means the ambient atmospheric gas space into whichexhaled gas enters after passing through and beyond the mask body and/orexhalation valve;

“filter cartridge” means a structure that is primarily designed to housea filter material or filter media and that is adapted for connection toa mask body of a personal respiratory protection device;

“filter material” or “filter media” means a structure or combination ofparts or elements adapted to provide clear air;

“housing” means a structure or combination of parts that is fashionedfor containing another item;

“integral” means that the parts in question are made together at thesame time and are not two separate parts subsequently brought together;

“interior gas space” means the space between a mask body and a person'sface;

“juxtaposed” or “juxtapositioned” means placed in a general side-by-siderelationship but not necessarily in contact with each other;

“mask” (when not referring to a “mask body” means having the ability torestrict the view of an object on the opposing side of the mask;

“opaque” means restricting the passage of visible light significantlymore than something that is transparent;

“pane” means a planar transparent area of a window which may or may notbe permeable to air;

“registration position” means the desired position of the window toprovide the appropriate response signal;

“response signal” means the viewable indication that tells the viewerthat the time to replace the filter cartridge has arrived;

“sorbent” means a material that is capable of capturing, occluding, oraltering a contaminant through absorption, adsorption, chemisorption,decomposition, reaction, catalysis, or other suitable means;

“transparent” means that visible light can pass therethroughsufficiently to see the desired image on the opposing side of thestructure modified by the word “transparent”; and

“window” means a structure that provides the ability for a person to seethrough.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a respirator 10 in accordance with thepresent invention.

FIG. 2 is a perspective view of a filter cartridge 12 in accordance withthe present invention.

FIG. 3 is a cross-section of the filter cartridge 12 shown in FIG. 2taken along lines 3-3.

FIG. 4 is a rear view of the filter cartridge 12 shown in FIGS. 1-3.

FIG. 5 is an enlarged cross-section of the housing 22 and the coverextension 36.

FIG. 6 is a cross-section of an ESLI 60.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a respirator 10 that has filter cartridges 12 that can besecured to opposing sides of the mask body 14. The mask body 14 isfashioned to snugly fit on a wearer's face. To this end, the respirator10 includes a harness 16 for drawing the mask body 14 towards thewearer's face. The harness 16 may include one or more straps 18 for thispurpose. The straps 18 may be joined to the mask body 14 and may beadjusted in length through use of buckles 20. The filter cartridges 12may be attached to the mask body 14 by bayonet attachments 21, threadingmeans, or any other suitable means for securing the cartridge 12 to themask body 14. The filter cartridges 12 have a housing 22 and a cover 24,which contain a filter media for filtering ambient air that is drawninto the mask interior through the filter cartridge 12. Air that isexhaled by the user passes from the interior gas space to the exteriorgas space through the exhalation valve 25.

FIGS. 2-4 illustrate that the filter cartridges 12 may include a housing22 that has a sidewall 26 that extends from a first perimeter 28 to asecond perimeter 30. The cover 24 may include an air throughput surface32 and a securement flange 34 located along a periphery of the cover 24.The cover 24 may be secured to the sidewall 26 at the housing perimeter28. The cover 24 may further include an opaque extension 36 thatincludes a window 38 located therein. The window 38 allows anend-of-service-life-indicator (ESLI) 40 to be seen therethrough. Thewindow 38 may have an opaque frame 39 located thereabout to drawattention to the window and to encourage ESLI viewing 90 degrees to theindicator. The extension 36 may be made opaque through selection ofmaterials that comprise the cover, for example, plastic resin or dyechoice or through printing an opaque medium on the inner or outersurface of the extension 36. The whole extension 36 does not need to beopaque in order for the extension 36 to be deemed opaque. Only, forexample, a portion sufficient to define the window needs to be opaque.Thus, at least some part of the extension 36 is opaque; other portionsmay be transparent. The extension 36 may extend away from the securementflange 34 of the cover 24 such that it resides over a substantialportion of the depth of the whole housing sidewall 26. Alternatively,the extension 36 may extend from the securement flange 34 on only one ortwo segments 37 of the flange 34. Thus, first and second extensions maybe provided over opposing portions 41, 41′ (FIG. 4) of the housingsidewall 26. The extension 36 may be configured to be about 3 to 6centimeters (cm) long by about 1 to 2 cm wide (depth). In providing awindow pane in the housing sidewall 26, the sidewall may be transparentthroughout much of its whole surface or only in the vicinity of the ESLI40 so that a person looking through the window 38 does not have anobstructed view of the ESLI 40. The ESLI may be juxtapositioned againstan inner surface of the housing sidewall 26. The window 38 thus may havea first pane located in the opaque extension 36 and a second panelocated in the housing sidewall 26. The first window pane may be an openpane that permits air transfer, whereas the second pane may be a solidpane impermeable to gas transfer. Additionally, a plurality of windows38 may be used in one or more extensions to allow a plurality of ESLIsto also be used, whereby each ESLI addresses a different contaminantsuch as acid gases, ammonia, formaldehyde, and organic vapors or adifferent organic vapor contaminant concentration—see U.S. patentapplication Ser. No. ______, entitled Multilayer Colorimetric SensorArrays (attorney case number 65359US002) filed on the same day as thispatent application. The window pane(s) when viewed normal thereto maytake on a variety of shapes in addition to circular, for example,rectangular, elliptical, triangular, pentagonal, hexagonal, heptagonal,octagonal, etc.

During filter cartridge use, ambient air travels through a series ofintake ports 43 located in the air throughput surface 32. This air thenpasses through the filter material 42 where contaminants present in theambient air are removed. In passing through the filter material 42, theair first enters the filter material 42 at first major surface 45 andexits it at second major surface 47. After passing through the filtermaterial 42, the air may enter a plenum 44 juxtaposed against the base46 of the filter cartridge 12. Air present in the plenum 44 then passesthrough the filter cartridge exit port 48. The filtered air may thenenter the interior gas space of the mask body 14 where it may be inhaledby the respirator wearer. As the air travels through the filtercartridge, contaminants that are present in the air interact with theESLI. Once a sufficient concentration of contaminants has interactedwith the ESLI, it will change color. The color change may be in the formof a gradient, and therefore it may be desirable to mask off the colorchanges that are not needed to be seen. Accordingly, the window 38provided for this purpose must be appropriately positioned along thesidewall 26 of the housing 22. The positioning of the window 38 maydepend on the particular ESLI that is being used, the activeparticulate, the location of the ESLI and active particulate within thefilter cartridge 12, and governmental (e.g. NIOSH) requirements. Thewindow registration position may be disposed axially in the y dimensionof the cartridge between the first and second major surfaces 45, 47 ofthe filter material 42. In some embodiments, the registration positionmay be located approximately midway between the first and second majorsurfaces 45, 47 of the filter material 42, whereas in other embodimentsthe registration position may be disposed axially closer to the secondmajor surface 47 than the first major surface 45.

Some ESLIs may appear to have a different color when not viewed 90degrees from the indicator. To preclude reader error from suchnon-normal viewing and to allow for sufficient visibility of theindicator, the window, as shown in FIG. 5, is preferably configured sothat the ESLI only can be viewed through a cone of visibility defined byan angle omega θ that is about 20 to 70 degrees, typically about 30 to60 degrees, and still more typically about 45 to 55 degrees. Angle θ isthe angle between a line 51 that extends normal from the window to aline 53 offset laterally from that line 51 to where the ESLI can nolonger be seen through the window 38. The window typically will have adiameter d of about 2 to 10 millimeters (mm), more commonly about 3 to 5mm. The thickness t of the window may be from about 1.2 to 12 mm, moretypically about 3 to 6 mm. The ratio of window thickness t to windowdiameter d (aspect ratio) typically is about 0.1 to 6, more typically0.5 to 3, and still more typically about 1 to 1.5. The surface or openarea of the window typically is about 3 to 1000 mm², more commonly 7 to20 mm². The cover extension 36 preferably is integral to the cover 24 sothat the masking feature can be provided at the same time that the cover24 is manufactured. A reference indicator 52, which has a shape similarto the shape of the window pane on the opaque extension 36, may beplaced on the extension 36 adjacent to the window 38 so that the wearercan identify the particular color, hue, and/or reflectivity of the ESLI,which indicates the need to change the filter cartridge.

In manufacturing a filter cartridge in connection with the presentinvention, the filter cartridge housing, filter media, and cover may bemanufactured using presently-known or later developed techniques. Thefilter cartridge housing and cover may be made using a injection moldingoperations. A first scrim 54 may be positioned at the top of the plenum44 before introducing the filter material 42. The filter material 42 maybe a filter material that removes gaseous or vapor contaminants and thatcomprises active particulate that is capable of sorbing one or moreundesired contaminants. The sorptive media may include a variety ofactive particulate such as activated carbon and alumina. U.S. Pat. No.7,309,513 to Brey et al., U.S. Pat. No. 5,696,199 to Senkus et al., U.S.Pat. No. 5,496,785 to Abler et al., and U.S. Pat. No. 5,078,132 to Braunet al., for example, describe various types of active particulate thatcould be used in connection with the present invention. The activeparticulate may be in the form of a packed or bonded bed—see, forexample, U.S. Pat. No. 5,033,465 to Braun et al., and U.S. Pat. No.6,391,429 to Senkus. The ESLI 40 may be placed against the inner surfaceof the housing sidewall 26 before active particulate introduction. TheESLI needs to be properly positioned relative to the y dimension so thatthe appropriate color change is seen through the window 38 when thefilter service life has ended. Small deviations in positioning along they axis can result in large differences in the response signal. A secondscrim 56 may be placed on the upstream surface 45 of the filter material42. The upstream scrim 56 may comprise a suitable fibrous medium thathelps retain the active particulate in place and provides a low pressuredrop thereacross and helps adequately distribute the air that passesthrough it. Examples of materials that may be used for scrims 54 and 56include nonwoven polyesters and nonwoven polypropylenes such as spunbondwebs. After the filter material 42 and scrims 54 and 56 have beenproperly positioned in the cartridge housing 22, the cartridge cover 24may be secured to the housing sidewall 26. The securement may beachieved at flange 34, for example, by mechanical, chemical, or physicalmeans including welding or adhesive bonding, or any other suitablemeans. When the cover 24 is positioned on the housing 22 such that thefilter cartridge 12 is properly assembled, the window 38 will be in itsproper registration position. The invention thus allows suchregistration to be achieved using manufacturing techniques that arecommonplace in the industry and that enable consistent reproduciblepositioning of the window.

ESLIs that may be used in connection with the present inventionpreferably are passive sensors that absorb or adsorb gas vapors that aredesired to be filtered from the air. The ESLI may be essentially anyknown or later developed device (passive or active) that is capable ofproviding the proper indication to the respirator wearer that the filterhas met the end of its useful life. Examples of passiveend-of-service-life-indicators have been described in U.S. PatentPublications 2000/0063575A1 and 2008/0063874A1 to Rakow et al. ESLIsthat may be employed include those that respond to organic vapors,reactive gases such as acidic (for example, SO₂, Cl₂, HCl, HCN, HF, H₂Sand oxides of nitrogen) and basic gases (for example, ammonia,methylamine), and cynogen chloride and formaldehyde.

As shown in FIG. 6, these end-of-service-life-indicators 60 may comprisea thin film multi-layer construction that can sorb a vapor of interestflowing from the gas inlet to the gas outlet of the respirator filtercartridge. Such passive ESLIs typically contain a porous detection layer62, a semi-reflective layer 64, and a reflective layer 66. The porousdetection layer 62 has a thickness that will change in the presence of aparticular vapor. The semi-reflective layer 64 is viewable from theoutside of the ESLI and is generally not permeated by the vapor. Thereflective layer 66 is generally permeable to the vapor and is insufficient proximity to the filter media such that the vapor can passthrough the reflective layer into the detection layer 62 and change thedetection layer optical thickness sufficiently to cause a visiblydiscernible change in the indicator appearance as viewed through thesemi-reflective layer 64.

An ESLI that is used in connection with the present invention may berigid or flexible. It can be secured to the housing cartridge interiorby various means such as adhesive, physical, packing techniques, ormechanical engagement. Flexible indicators desirably are sufficientlybendable without fracturing so that they can be made using one or moreroll processing steps.

The ESLI may include an optional substrate 68 such as glass or aflexible plastic film that may be handled in one or more roll processingsteps. The substrate desirably has sufficiently low vapor permeabilityso that the vapor(s) of interest will not be transmitted into or out ofthe ESLI detection layer. A porous substrate may be placed between thereflective layer and the sorbent media. For example, vapors of interestcould be allowed to pass from the sorbent media through the permeablesubstrate and reflective layer and thence into the detection layer. Theoverall thickness of the ESLI (excluding a substrate) may be about 0.5to 2 micrometers (μm).

The semi-reflective and reflective layers each may be made from avariety of materials that provide diffuse or preferably specular lightreflection and that can cooperate when appropriately spaced apart toprovide a readily visibly perceptible indicator appearance change.Suitable semireflective and reflective layer materials include metalssuch as aluminum, chromium, gold, nickel, silicon, silver, palladium,platinum, titanium and alloys containing such metals; metal oxides suchas chrome oxide, titanium oxide and aluminum oxide; and the multilayeroptical films (including birefringent multilayer optical films)described in U.S. Pat. No. 5,699,188 (Gilbert et al.), U.S. Pat. No.5,882,774 (Jonza et al.) and U.S. Pat. No. 6,049,419 (Wheatley et al.),and PCT Published Application No. WO 97/01778 (Ouderkirk et al.). Thesemireflective and reflective layers may be the same or different. Metalnanoparticle coatings (e.g., metal nanoparticle inks) may be employed toform the reflective layer, as described in U.S. patent application Ser.No. 11/530,619 entitled Permeable Nanoparticle Reflector.

The semireflective layer is less reflective than the reflective layerand transmits some incident light. The semireflective layer may, forexample, have a physical thickness of about 2 to about 50 nanometers(nm), light transmission at 500 nm of about 20 to about 80%, andreflectance at 500 nm of about 80 to about 20%. The semireflective layermay itself be impermeable to vapor (and if so desirably is continuous)and optionally coated on or otherwise adjacent to a suitable substrate.The semireflective layer also may be permeable to vapor (and if so may,for example, be discontinuous or semicontinuous) and coated on orotherwise adjacent to a suitably vapor-impermeable substrate. The faceof the semireflective layer adjacent the detection layer desirably isflat to within about ±10 nm.

The reflective layer may, for example, have a physical thickness ofabout 1 to about 500 nm, light transmission at 500 nm of about 0 toabout 80%, and reflectance at 500 nm of about 100 to about 20%. Thereflective layer preferably is porous, patterned, discontinuous,semicontinuous or otherwise sufficiently permeable so that vapor canpass from the sorbent media through the reflective layer into thedetection layer.

The detection layer mixture may be homogeneous or heterogeneous, andmay, for example, be made from a mixture of inorganic components, amixture of organic components, or a mixture of inorganic and organiccomponents. Detection layers made from a mixture of components mayprovide improved detection of groups of analytes. The detection layerdesirably has a range of pore sizes or a surface area selected toprovide vapor sorption characteristics like those of the sorbent media.Suitable porosity can be obtained using porous materials such as foamsmade from high internal phase emulsions, such as those described in U.S.Pat. No. 6,573,305 B1 (Thunhorst et al.). Porosity may also be obtainedvia carbon dioxide foaming to create a microporous material (see“Macromolecules”, 2001, vol. 34, pp. 8792-8801), or by nanophaseseparation of polymer blends (see “Science”, 1999, vol. 283, p. 520). Ingeneral, the pore diameters preferably are smaller than the peakwavelength of the desired indicator coloration. Nano-sized pores arepreferred, e.g., with average pore sizes of about 0.5 to about 20 nm,0.5 to about 10 nm, or 0.5 to about 5 nm.

Representative inorganic detection layer materials include poroussilica, metal oxides, metal nitrides, metal oxynitrides and otherinorganic materials that can be formed into transparent and porouslayers of appropriate thickness for producing color or a colorimetricchange by optical interference. For example, the inorganic detectionlayer materials may be silicon oxides, silicon nitrides, siliconoxynitrides, aluminum oxides, titanium oxides, titanium nitride,titanium oxynitride, tin oxides, zirconium oxides, zeolites orcombinations thereof. Porous silica is an especially desirable inorganicdetection layer material due to its robustness and compatibility withwet etching treatments.

Representative porous silica materials are described in Ogawa et al.,Chem. Commun. pp. 1149-1150 (1996), in Kresge et al., Nature, Vol. 359,pp. 710-712 (1992), in Jia et al., Chemistry Letters, Vol. 33(2), pp.202-203 (2004) and in U.S. Pat. No. 5,858,457 (Brinker et al.). Avariety of organic molecules may also be employed as organic templates.For example, sugars such as glucose and mannose may be used as organictemplates to generate porous silicates, see Wei et al, Adv. Mater. 1998,Vol. 10, p. 313 (1998).

Representative organic detection layer materials include polymers,copolymers (including block copolymers) and mixtures thereof prepared orpreparable from classes of monomers including hydrophobic acrylates andmethacrylates, difunctional monomers, vinyl monomers, hydrocarbonmonomers (olefins), silane monomers, fluorinated monomers, hydroxylatedmonomers, acrylamides, anhydrides, aldehyde-functionalized monomers,amine- or amine salt-functionalized monomers, acid-functionalizedmonomers, epoxide-functionalized monomers and mixtures or combinationsthereof U.S. Patent Application Publication No. US 2004/0184948 A1contains an extensive list of such monomers. The above-mentionedpolymers having intrinsic microporosity (PIMs) provide particularlydesirable detection layers. PIMs typically are non-network polymers thatform microporous solids. Due to their typically highly rigid andcontorted molecular structures, PIMs are unable to fill spaceefficiently, thus providing the disclosed microporous structure.Suitable PIMs include, but are not limited to, polymers disclosed in“Polymers of intrinsic microporosity (PIMs): robust,solution-processable, organic microporous materials,” Budd et al., Chem.Commun., 2004, pp. 230-231. Additional PIMs are disclosed in Budd etal., J. Mater. Chem., 2005, 15, pp. 1977-1986, in McKeown et al., Chem.Eur. J. 2005, 11, No. 9, 2610-2620 and in Published PCT application No.WO 2005/012397 A2 (McKeown et al.).

The thickness of the detection layer may also be patterned, for example,as described in U.S. Pat. No. 6,010,751 (Shaw et al.). The pattern maydisappear (for example when a thinner portion swells to the samethickness as a thicker portion) or appear (for example, when a portionshrinks to a lesser thickness than an adjacent portion). When providinga reference indicator that would allow the wearer to easily identifywhen the trip point has been reached, the detection layer thickness canbe altered to achieve an appearance that is identical to the trippingpoint of the ESLI. Alternatively, an ESLI reference that is structurallyidentical to the ESLI that would be seen through the window of thepresent invention can be forced to its response signal and preserved inthat condition. Or the detection layer may be made thicker so that thereference ESLI displays the desired response signal. This preserved ESLImay be placed on the exterior of the filter cartridge as a referenceindicator so that a comparison can be made between it and the image seenthrough the window. When the ESLI that is seen through the windowappears to be the same as the reference indicator, the wearer knows thatthe filter cartridge has met the end of its service life. It is alsopossible to print a reference color that matches or approximates the endstate of the sensor using an appropriate dye or pigment.

The ESLI may include additional layers or elements if desired. Forexample, a porous layer of sorbent-loaded composite (e.g., a web ofactivated carbon particles ensconced in a matrix of fibrillated PTFEsuch as is described in the above-mentioned U.S. Pat. No. 4,208,194) maybe placed between the reflective layer and the sorbent media, tohomogenize vapors permeating into the indicator or otherwise moderatethe indicator response to conditions in the sorbent media. When the ESLIchanges to the color or hue that indicates that the filter cartridgeshould be replaced, the change in such appearance reflects a specifiedlevel of sorbent depletion that mandates replacement of the filtercartridge. In other words, the manufacturer of the filter cartridge mayadjust the selection of the particular ESLI and the positioning of thewindow into its registration position such that the particular level ofsorbent depletion can be achieved. The selection of the level of sorbentdepletion may depend on a variety of factors, including providing asufficient buffer so that the sorbent is not 100% depleted when thefilter cartridge is identified as being needed to be replaced. The levelof sorbent depletion may, for example, be identified to provide one tothree hours of additional use so that the wearer has adequate time tonotice that the ESLI has undergone the color change indicatingsatisfaction of the response signal or need for cartridge replacement.

The filter cartridge also may include one or more layers of filter mediafashioned for removing particulates. Fibrous particulate filters may beused upstream or downstream to the active particulate to removeparticulate contaminants from the ambient air. A variety of fibrous websmay be suitable for use as particulate filters. These webs typically arenonwoven fibrous structures that can be made from techniques such asair-laid processes, wet-laid processes, hydro-entanglement, spunbondprocesses, and meltblown processes such as described in Van A. Wente,Superfine Thermoplastic Fibers, 48 INDUS. ENGN. CHEM. 1342-46 and inReport No. 4364 of the Naval Research Laboratories, published May 25,1954, entitled Manufacture of Super Fine Organic Fibers by Van A. Wenteet al. The fibrous webs can be made using combinations of thesetechniques and combinations of such fibers. Microfibers, particularlymeltblown microfibers, are particularly suitable for use in fibrous websthat are used as filters. As used in this document, “microfiber” meansfiber(s) that have an effective diameter of about 35 micrometers orless. Effective fiber diameter can be calculated using equation number12 in Davies, C. N., The Separation of Airborne Dust and Particles,INST. MECH. ENGN., LONDON PROC. 1B (1952). For filtering applications,the microfibers typically have an effective fiber diameter of less thanabout 30 micrometers, more typically, about 1 to about 15 micrometers.Fibers made from fibrillated films may also be used—see, for example,U.S. Pat. Nos. RE30,782, RE32,171, 3,998,916 and 4,178,157 to VanTurnout. Nonwoven webs that are made by the process of the presentinvention may exhibit quality factors QF that exceed 2, 2.1, 2.2, and2.3.

Staple fibers also may be combined with the microfibers to improve webloft, that is, to reduce its density. Reducing web density can lower thepressure drop across the web, making it easier for air to pass throughthe filter. Lower pressure drops are particularly desirable in personalrespiratory protection devices because they make the respirator morecomfortable to wear. When the pressure drop is lower, less energy isneeded to draw air through the filter. A respirator wearer who dons anegative pressure mask—that is a respirator that requires negativepressure from the wearer's lungs to draw air through the filter—does nothave to work as hard to breath filtered air. Lower energy requirementsalso can be beneficial in powered filtering systems to reduce costsassociated with powering the fan and to extend the service life of abattery in a battery powered system. In a typical nonwoven fibrousfilter, no more than about 90 weight percent staple fibers are present,more typically no more than about 70 weight percent. Often, theremainder of the fibers are microfibers. Examples of webs that containstaple fibers are disclosed in U.S. Pat. No. 4,118,531 to Hauser.

Although the present invention has been illustrated using a full-facerespirator mask that covers the wearer's nose, mouth, and eyes, thepresent invention also may be used in conjunction with half-masks thatcover only the wearer's nose and mouth. Further, the filter cartridgesthat are used in connection with the present invention may bepermanently or removably attached to the mask body. Additionally, therespirator may have one or more filter cartridges that are attachable tothe mask body. The harness also may come in a variety of configurationsand may include additional parts such as a crown member to support therespirator on a wearer's head. Accordingly, a variety of embodiments arecontemplated by the invention when providing respirator masks that haveend-of-life-service-indicators disposed on the filter cartridge.

EXAMPLE ESLI Preparation

In a 2.0 liter (L) three-neck round bottomed flask, 33.4357 grams (g) of3,3,3′,3′-tetramethyl-1,1′-spirobisindane-5,5′,6,6′-tetrol (tetrol) and19.8016 g of tetrafluoroterephthalonitrile (TFTN) were dissolved in 900milliliters (mL) of anhydrous N,N-dimethyl formamide (DMF). The solutionwas stirred with a mechanical stirrer, and nitrogen was bubbled throughthe solution for one hour. To this solution was added 81.4491 g ofpotassium carbonate. The flask was placed in an oil bath at 68° C. Themixture was stirred at this elevated temperature under a nitrogenatmosphere for 65 hours. The polymerization mixture was poured into 9.0L of water. The precipitate formed was isolated by vacuum filtration andwashed with 600 mL of MeOH. The isolated material was spread out in apan and allowed to air dry overnight. The solid was placed in ajar anddried under vacuum at 68° C. for 4 hours. The resulting yellow powderwas dissolved in 450 mL of THF. This solution was poured slowly into 9.0L of methanol. The precipitate formed was isolated by vacuum filtration.The isolated material was spread out in a pan and allowed to air dryovernight. The solid was placed in ajar and dried under vacuum at 68° C.for 4 hours. The precipitation in methanol was performed one more time.The resulting dried, bright yellow polymer weighed 42.80 g. Analysis ofthe polymer by GPC using light scattering detection showed the materialto have a M_(n) of approximately 30,900.

A metalized polyethylene terephthalate (PET) substrate was prepared byevaporatively depositing a 10 nm-thick Ni metal layer onto Melinex ST505clear PET. A 4% by weight solution of TFTN-PIM in chlorobenzene wasprepared and solution deposited onto the Ni-coated PET by spin coating,to a thickness of approximately 600 nm. A silver nanoparticle layer wassolution deposited onto the TFTN-PIM layer using 100 g of stocknanosilver suspension (DGP-40LT-15C from Advanced Nanoproducts, Korea,40% by weight silver in methanol) diluted with 100 g of1-methoxy-2-propanol. The silver suspension was spin coated onto the PIMlayer. After deposition, the overall sensor construction was heated at150 degrees C. for 1 hour to sinter the silver nanoparticles. Theresulting thin-film indicator had a green appearance when visuallyobserved normally through the clear PET substrate.

Cartridge Assembly

A filter cartridge housing was molded from clear styrene (K-Resin fromChevron-Phillips). A scrim made from Remay™ spunbond polyester(available from Fiberweb of London, United Kingdom) was welded intoplace in the bottom of the housing. An optical transfer adhesive (3MOptically Clear Adhesive 8172 from 3M Company) was used to adhere theindicator to the transparent inner wall of the housing by making a bondbetween the PET and the cartridge sidewall. The remaining filtrationcartridge volume was then filled with 45.8 g of activated carbon sorbent(GG carbon from Kuraray Corp., at 12×20 mesh size).

A cartridge inlet cover having an extension as shown in FIGS. 1-3 andwas made using a rapid-prototype ABS plastic. A second scrim also madefrom Remay™ spunbond polyester was glued to the inner surface of thecover. The cover-scrim assembly was then sonically welded to thehousing, compressing the carbon in the process. The window had athickness t of about 5 mm, a diameter d of about 4.2 mm, a surface areaof about 13.9 mm², and a cone angle of visibility θ of about 50 degrees.The resulting cartridge exhibited an ESLI that appeared green in colorwhen seen through the window before any exposure. The indicator was outof view when the cartridge was tilted such that the viewer's line ofsight was outside angle θ.

This invention may take on various modifications and alterations withoutdeparting from its spirit and scope. Accordingly, this invention is notlimited to the above-described but is to be controlled by thelimitations set forth in the following claims and any equivalentsthereof.

This invention also may be suitably practiced in the absence of anyelement not specifically disclosed herein.

All patents and patent applications cited above, including those in theBackground section, are incorporated by reference into this document intotal. To the extent there is a conflict or discrepancy between thedisclosure in such incorporated document and the above specification,the above specification will control.

1. A filter cartridge that comprises: (a) a filter material; (b) anend-of-service-life-indicator (ESLI); (c) a cartridge housing into whichthe filter material and ESLI are disposed; (d) a window through whichthe ESLI may be viewed, the window being configured such that the ESLIcan only be seen through the window within a cone defined by an angle θof 20 to 70 degrees.
 2. The filter cartridge of claim 1, wherein angle θis 30 to 60 degrees.
 3. The filter cartridge of claim 1, wherein angle θis 45 to 55 degrees.
 4. The filter cartridge of claim 1, wherein thewindow is circular and has a diameter of 2 to 10 mm.
 5. The filtercartridge of claim 1, wherein the window is circular and has a diameterof 3 to 5 mm.
 6. The filter cartridge of claim 1, wherein the window hasa thickness t of 1.2 to 12 mm.
 7. The filter cartridge of claim 1,wherein the window has a thickness t of 3 to 6 mm.
 8. The filtercartridge of claim 1, wherein the window has an aspect ratio of 1 to 6.9. The filter cartridge of claim 1, wherein the window has an aspectratio of 0.5 to
 3. 10. The filter cartridge of claim 1, wherein thewindow has an aspect ratio of 1 to 1.5.
 11. The filter cartridge ofclaim 1, wherein the window has a surface area of about 3 to 100 mm².12. The filter cartridge of claim 1, wherein the window has a surfacearea of about 7 to 20 mm².
 13. The filter cartridge of claim 1, whereinthe window has a frame located about a window pane.
 14. The filtercartridge of claim 13, wherein the cartridge housing has a sidewall thatis transparent in the vicinity of the window.
 15. The filter cartridgeof claim 14, wherein the window has first and second panes, the firstpane being disposed in the housing sidewall and the second pane beingdisposed in an extension of a cover that is attached to the cartridgehousing.
 16. The filter cartridge of claim 15, wherein the pane that isdisposed in the cartridge housing sidewall is fluid impermeable, andwherein the pane that is disposed in the cover extension is fluidpermeable.
 17. The filter cartridge of claim 1, wherein the windowcomprises a frame located about a window pane.
 18. A mask body that isadapted to fit at least over a person's nose and mouth and thatcomprises one or more of the filter cartridges of claim 1, attachablethereto.
 19. A respirator that comprises the mask body of claim
 18. 20.A respirator that comprises a mask body; a harness attached to a maskbody; one or more filter cartridges that are attachable to the maskbody; the cartridges comprising a housing into which a filter materialand an ESLI are disposed. A housing into which the filter material isdisposed, the housing has a sidewall onto which the ESLI is juxtaposedagainst. The housing further including a cover through which air maypass before it being filtered by the filter material, a window beingpositioned in the vicinity of the ESLI so that the ESLI can be seentherethrough, the window being adapted to provide a viewer with a coneof visibility that is defined by an angle θ of 20 to 70 degrees, thewindow further having an aspect ratio of 0.5 to 3, a thickness of 1.2 to12 mm, and a surface area of 7 to 20 mm².